Xmind brainstorming and mind mapping software supports numerous formats for export of project files (.xmind), including HTML format so in this sense xmind to html conversion is certainly doable. Unfortunately Xmind formats are notoriously not supported in alternative/competitive products, so using the original software is your only option. You can always try out the trial version and see if you can do a quick export of the mind map that way.
Updated: August 30, 2023